There may be a need for the n-well, which can contain the components such as resistors, capacitors, Z-diodes and MOS-transistors in bipolar and CMOS designs, to have a terminal with resistance to polarity reversal. Several techniques are known for achieving such a terminal with resistance to polarity reversal.
a) It is possible to provide a so-called floating well, in which although resistance to polarity reversal is ensured and it is also possible to accommodate other components, high leakage currents occur, in particular at relatively high temperatures. P-regions in this well can function as collectors or as well-carrying emitters. Such a p-region in the n-well becomes the emitter of a parasitic pnp-transistor whose collector current is the leakage current which flows between the n-well and the surrounding p-region. PA1 b) A further possibility of achieving resistance to polarity reversal consists in connecting a collector element of a pnp-transistor to the n-well. However, this involves increased outlay on production and wiring, since the pnp-transistor has to be accommodated in a separate second well. PA1 c) Resistance to polarity reversal can also be achieved by driving the well below the positive potential of the operating voltage (U.sup.+), by a diode voltage, by interposing a pnp-diode. It is disadvantageous in this solution that the injection through other p-regions connected to U.sup.+ cannot be completely prevented. In addition, a large area requirement is produced, in turn, in the case of production. PA1 d) A further possibility consists in applying U.sup.+ to the well via a resistor. In this case, however, in the event of polarity reversal there is a flow of current resulting from the resistance value. However, there is likewise a need for a relatively large area because of the relatively high resistance of the resistor.